Throughout the history of the dental profession, dental professionals have used a variety of tooth restoration materials in an attempt to effectively restore tooth structure, for example, for filling a cavity. One example of a now antiquated tooth restoration material is a compressed mercury-silver alloy known as an amalgam. Amalgam was once the more popular choice of tooth restoration materials due to the ability of the amalgam to provide a long term tooth restoration material solution.
Different from more modem tooth restoration materials, as will be discussed further below, a dental professional secures the amalgam into place without bonding the amalgam directly to the tooth substrate. Instead, amalgams are usually held in place within the tooth structure by compressing the amalgam into a mechanically retentive cavity formed within the tooth. For example, most amalgams require the dental professional to cut cavity preps to create mechanical undercuts within the tooth structure that physically hold the amalgam within the tooth cavity.
Due to the fact that amalgams do not actually bond directly to the tooth structure, oral fluids, microbes, foods and other substances found in the oral cavity are able to migrate or leak between the amalgam and the tooth structure. The migration of oral fluids, microbes, and food between the amalgam and the tooth structure would normally create an ideal situation for continued tooth decay, but amalgams contain silver and mercury, which continue to leach out from the amalgam, and in effect sterilize the cavity prep from further decay. The elemental and ionic forms of both silver and mercury can act as anti-microbial agents, and therefore, amalgams can control long-term tooth decay between the amalgam and tooth structure.
Although amalgams can control long-term tooth decay between the amalgam and the tooth structure, amalgams have a variety of disadvantages that have caused dental professionals to move away from the use of amalgams as a tooth restoration material. For example, one disadvantage of amalgams is that amalgams are not aesthetically pleasing because the opaque silver/black color of the amalgam contrasts greatly with the remaining white tooth. In general, patients generally feel that amalgam tooth restoration materials have a negative aesthetic appearance compared to the aesthetic appearance of the tooth before the amalgam is placed.
Another disadvantage of using amalgams is that in order for the dental professional to properly form the cavity preps, as generally described above, the dental professional is often required to remove an excessive amount of tooth structure than is preferred in order to correctly place an amalgam, including removing healthy tooth structure. In general, dental professionals always attempt to remove as little of healthy tooth structure as possible in order to maintain the integrity of the tooth, which can lead to a longer lasting tooth over the lifetime of a patient.
Despite the above and other disadvantages, dental professionals used amalgams for many years because suitable alternatives did not exist. More recently, however, additional tooth restoration materials were introduced in an attempt to overcome some of the disadvantages associated with amalgams. These additional tooth restoration materials may include primers, adhesives, cements, composites, and other direct or indirect materials. For example, more modem tooth restoration materials overcome the need for the dental professional to remove excessive tooth structure material, as required by amalgams, and allow for the use of tooth-colored filling materials.
As an overview, for example, the process of placing more modern tooth restoration materials includes the use of a tooth etching material, an adhesive, and a tooth-colored composite filling material. First, the tooth is etched with an acid to chemically remove the smear layer of dentin and surface-roughen the enamel of the cavity prep. Second, a low viscosity liquid adhesive is applied to the etched surface and allowed to penetrate into the tooth followed by polymerizing the adhesive into a solid polymer. Third, the remaining cavity is filled with a tooth-colored composite and polymerized/cured into a solid mass by means of various methods such as light curing with a light source. Since the modern tooth restoration materials bond directly to tooth structure, the dental professional does not need to remove excessive tooth structure. Moreover, the color of the modem tooth restoration materials can be controlled, providing an aesthetic advantage that causes the tooth restoration material color to closely match the color of the original tooth structure.
Notwithstanding the ability of the more modem tooth restoration materials to overcome the advantages of amalgams, the more modem tooth restoration materials also have various disadvantages. For example, many modern tooth restoration materials are made from organic compounds that may contain fairly inert non-toxic fillers (e.g., various powdered glasses). These tooth restoration materials are designed to be non-toxic, and are therefore unlike amalgams, are not sufficiently anti-microbial such that they can control decay between the restoration and tooth structure.
Furthermore, many modern tooth restoration materials require a polymerization process that will cause shrinkage of the filling material during the curing process. When these tooth restoration materials shrink, a gap between the tooth and restorative material may form that allows leakage to occur between the tooth structure and the tooth restoration materials. Due to the gap that forms, and the subsequent leakage, the tooth that was filled may begin to decay again because the more modem tooth restoration materials do not have anti-microbial properties.
In sum, metal amalgams are plagued with an unpleasant dark color, are made from toxic materials, and require excessive removal of tooth structure; yet, notwithstanding these deficiencies, do not suffer from recurrent decay after long-term tooth placement. On the other hand, more modern tooth restoration materials are tooth colored and non-toxic; yet, notwithstanding these advantages, suffer from recurrent decay after placement.
Accordingly, there are a number of disadvantages in the conventional art of tooth restoration materials.